Dutasteride
Avodart
Blocks both 5-alpha-reductase isoenzymes instead of one, regrows more hair than finasteride in head to head trials, and carries a half-life measured in weeks rather than hours.
FDA-approved
FDA-approved in 2001 for benign prostatic hyperplasia. Not FDA-approved for hair loss, though it is approved for androgenetic alopecia in South Korea and Japan and prescribed off-label for it elsewhere.
What it is
There are two isoenzymes of 5-alpha-reductase that convert testosterone into dihydrotestosterone. Finasteride inhibits type 2. Dutasteride inhibits both type 1 and type 2, and suppresses circulating DHT by well over 90% against roughly 70% for finasteride.
More suppression produces more hair. A trial of 917 men found dutasteride 0.5 mg significantly increased hair count and width at week 24 compared with both finasteride and placebo, and smaller randomised studies have reproduced the direction of that result consistently.
The trade is not free
Everything that makes finasteride controversial applies here with the dial turned up. If the mechanism causing sexual and mood side effects in a minority of finasteride users is DHT suppression, then suppressing DHT more thoroughly is not obviously the safer choice.
Head to head trials generally report similar adverse event rates between the two, which is the argument dutasteride advocates make. It is a fair argument and it has a limit: these trials are months long, powered for hair count, and not designed to detect uncommon persistent effects. See finasteride for why that debate has stayed unresolved for twenty years.
The half-life changes how mistakes work
Five weeks is an unusual number for a drug people take casually.
Finasteride clears in hours. If it disagrees with you, stopping produces an answer reasonably quickly. Dutasteride takes months to leave, and detectable levels persist longer still. Someone who develops a side effect at week three is committed to a long tail whether they stop or not.
That same property is why intermittent dosing is plausible at all. A randomised pilot compared twice-weekly and thrice-weekly dutasteride against daily finasteride and found thrice-weekly dutasteride produced greater moderate-to-marked improvement, 35% against 21%, without significantly beating finasteride on raw hair count. Interesting, small, and not a reason to invent your own schedule.
Practical notes
- The approval status varies by country and that is not a safety signal. South Korea and Japan approved it for androgenetic alopecia. The FDA approved it only for BPH. Both regulators saw similar data and made different calls about a cosmetic indication.
- Tell whoever orders your PSA. Both 5-alpha-reductase inhibitors roughly halve it. A PSA that looks reassuring can be masking a real value, and the correction is not something to leave to chance.
- Start with finasteride if you are starting at all. It is better characterised, shorter acting, and reversible on a human timescale. Escalating later is easy. Un-escalating is not.
Side effects and warning signs
Commonly reported
- Reduced libido, erectile difficulty or reduced ejaculate volume
- Breast tenderness or enlargement
- Mood changes, including depressive symptoms in some reports
- Lowers PSA substantially, which matters for prostate cancer screening
Stop and get medical help
- Pregnancy in a partner combined with handling of the capsules, since 5-alpha-reductase inhibitors can affect development of male genitalia
- New breast lump or nipple discharge
- Persistent depressive symptoms or suicidal thinking
Sources
From the community
Discussion for this compound concentrates in r/tressless and r/Hairloss.
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